Going to boot in 18 days; what’s most efficient way of improving run time?

Currently sitting at a 14:23 1.5 mile pace. What’s the quickest and most efficient way of getting that pace cut to where I need to for the IST? Pull ups and planks aren’t a problem as I can do 7 pull ups and a 3 minute plank. I just suck at running and breathing while I’m doing it at pace.